This invention relates generally to separable connection devices, and more particularly, to an improved non-pyrotechnic separable connector for minimizing shock during rapid separation.
Separation devices have long been used in a variety of applications to connect structures until it its desired to have the structures separate, and many such devices are known in the art. In many applications several separable connectors are used to form a connection and must be able to separate the connection simultaneously or nearly so. Thus, each of the separable connectors must accomplish separation quickly to prevent timing problems. However, in accomplishing a quick separation, some devices cause shock to occur duration separation. In some cases, the shock is due to the operation of the separable connector itself, such as in the case of pyrotechnically driven separable connectors. In other cases, the shock is due to the separable connector quickly releasing the strain energy stored in the connection, when the connection is under a high pre-load, without converting or diverting the strain energy in a harmless manner. In many applications the connection is under a significant pre-load to maintain stiffness or prevent gapping in the connection. The rapid release of chemical, mechanical, or strain energy from the connection can be harmful to surrounding components causing a host of problems in many applications such as optical and electrical component failure. Other problems associated with pyrotechnic release devices include increased safety cost, increased electrical cable shielding weight, and ordinance storage cost to name a few.
Some prior separable connectors have, for example, used a segmented nut which is explosively actuated to release a member to which it is engaged, causing a great deal of chemical energy to be released as shock during separation. One such device, disclosed in U.S. Pat. No. 3,405,593 to Kriesel, uses a pyrotechnic event to move a piston to break a frangible member holding a segmented nut together to cause the nut to separate and release its connecting member thus allowing separation. While separation occurs in a desirably brief period of time, approximately 7-10 milliseconds, this device, not only does not harmlessly direct strain energy released during separation, but also adds chemical energy to the system which is also rapidly released as shock during separation. Some devices have attempted to reduce the shock produced by rapid strain energy release through the gradual release of high pre-load force. For example, U.S. Pat. No. 4,410,293 uses a first pyrotechnic separation bolt assembly to release a split nut surrounded by a yieldable assembly to first release the pre-load, and a second pyro-technic separation bolt assembly to cause the final separation. However, this device also adds chemical energy to the system which is rapidly released during separation.
Other separation devices have been fashioned to provide non-pyrotechnically actuated separation of a segmented nut. For example, U.S. Pat. No. 5,221,171 uses a remotely controlled spring biased locking sleeve in which the spring is used to push the sleeve off the segmented nut to allow it to radially separate and thereby release its connecting member. While suitable for its purpose, this device still adds to the total energy of the connection system, in the form of mechanical energy of the spring, which also creates its own shock when released during separation. Additionally, as with pyro-technically actuated devices for which the amount of chemical energy necessary to separate the nut increases for larger pre-loads, larger amounts of spring energy are required for larger pre-loads to push the sleeve in this device.
Some prior art devices do utilize actuators which do not add a significant amount of energy to the total energy of the connection system. For example, U.S. Pat. No. 5,282,709 shows a separable connector which utilizes a segmented nut enclosed by a radially movable segmented spool bounded by a retaining wire which releasably holds the nut together without adding potentially harmful energy to the connection. One drawback to this device is that it either requires a large amount of electrical power for actuation or some means for external mechanical actuation. Another example is U.S. Pat. No. 5,160,233 which discloses a separable connector using a shape memory alloy to causes a piston to translate to allow separation. These devices, however, do not also address the problem of quick strain energy release during separation.
Other devices do attempt to eliminate strain release shock forces without adding harmful energy to the connection, such as by using shape memory alloys in a manner to relieve pre-load prior to separation. For example, U.S. Pat. No. 5,248,233 utilizes a shape memory alloy which is shrunken to relieve pre-load. In addition to other disadvantages, such as having a limited stroke to relieve the pre-load, this device does not provide a quick separation and the timing and speed problems associated with non-simultaneous separation exist when a plurality of these devices are used to form a separable connection.
It would be advantageous if a separable connector could be driven by the strain energy stored in the pre-loaded connection itself, rather than by adding excessive external energy to the connection system to drive the separation. It would further be advantageous for the separable connector to allow the stored strain energy to be released quickly yet diverted in such a manner so that minimal strain energy release shock is created during the separation. If would highly advantageous if the level of shock created during separation in the use of such a device was low enough to significantly reduce the need for conducting shock testing prior to use in a particular application, a time consuming and costly procedure. It would further be advantageous if the device was reusable so that the device itself could be functionally tested prior to use. It would further be advantageous if the device should be easily resetable without disassembly.